1. Field of the Invention
The present invention relates to a planar lightwave circuit module comprising a planar lightwave circuit provided with a plurality of input ports or a plurality of output ports and having a function of monitoring the powers of multi-channel signal light beams coming incident on the plurality of input ports or emitting from the plurality of output ports.
2. Related Background Art
In a planar lightwave circuit (PLC) having a plurality of input ports or a plurality of output ports, e.g., a multi-channel optical variable attenuator, optical demultiplexer, or optical multiplexer, it becomes necessary to monitor the powers of the signal light beams of respective channels coming incident on the respective input ports or emitting from the respective output ports. Because it is necessary for adjusting the powers of the signal light beams of respective output channels in the optical demultiplexer or adjusting the characteristics of the multiplexed signal light in response to the power of the input signal light beams in the optical multiplexer.
In order to monitor the powers of the signal light beams of the respective channels, a photocoupler is provided to an optical waveguide connected to the input ports or output ports. Part of the signal light beam is branched by the photocoupler to another optical waveguide, and the power of the branched signal light beam is monitored by a photodetector.
For example, a multi-channel optical variable attenuator using a Mach-Zehnder type optical waveguide is a PLC having a plurality of input ports and a plurality of output ports. FIG. 11 is a view showing an arrangement corresponding to one channel of such a conventional multi-channel optical variable attenuator. This one-channel optical variable attenuator has a PLC on a substrate 1, this PLC consists of an input optical waveguide 2, first directional coupler 3, first optical waveguide 4, second optical waveguide 5, second directional coupler 6, output optical waveguide 7, and monitoring optical waveguide 8. And the attenuator has a heater 9 for adjusting the temperature of the first optical waveguide 4 and a photodetector 10 connecting the exit end of the monitoring optical waveguide 8. The multi-channel optical variable attenuator is provided with such configured optical variable attenuators parallel aligned on the substrate 1.
In this optical variable attenuator, a signal light beam input to the input optical waveguide 2 is branched by the directional coupler 3. The branched signal light beams are input to the directional coupler 6 through the optical waveguides 4 and 5, respectively. These signal light beams are output from the directional coupler 6 to the output optical waveguide 7 and monitoring optical waveguide 8 with a predetermined branching ratio. This branching ratio is adjusted by controlling the temperature of the optical waveguide 4 with the heater 9 so as to change the optical path length of the optical waveguide 4. The power of the light beam emitting from the exit end of the monitoring optical waveguide 8 is detected by the photodetector 10, and the temperature of the optical waveguide 4 is controlled by the heater 9. Therefore, the ratio (Pout/Pin) of a power Pout of the signal light beam to be output to the output optical waveguide 7 to a power Pin of the signal light beam input to the input optical waveguide 2, i.e., the optical attenuation amount, can be controlled.
In addition, as a PLC having a plurality of input ports or a plurality of output ports, an AWG (Arrayed Waveguide Grating) used as an optical multiplexer or optical demultiplexer is well known. For example, a reference xe2x80x9cGeneral Meeting of Year 1996 of The Institute of Electronics, Information and Communication Engineers, B-1183xe2x80x9d describes an arrangement in which photodetectors are connected to ports, in an AWG serving as an optical demultiplexer, that output high-order diffracted light. In this AWG, the powers of the signal light beams of the respective wavelengths demultiplexed by the AWG are monitored on the basis of the detection results of the high-order diffracted light detected by the photodetectors.
In such conventional PLCS, monitoring optical waveguides must be separately provided in units of output ports. When multi-channel PLCs are integrated, the circuit configuration becomes complicated, and the module size increases. Although the monitoring signal light beam (demultiplexed light or high-order diffracted light) has characteristics which are different to those of the original exit signal light beam, the branching ratio may be fluctuated with the power of the original exit signal light beam. Therefor, the power of the original exit signal light beam cannot sometimes be monitored accurately.
The present invention has been made in order to solve the problems described above, and has as its object to provide a PLC module which can accurately monitor the power of signal light beams of the respective channels with a simple arrangement.
In order to solve the above-mentioned problems, the PLC module according to the present invention comprises (1) a PLC provided with many waveguides including a plurality of output optical waveguides on a substrate, wherein output end faces of the output optical waveguides are slant against the optical axis thereof; (2) an output optical fiber array including output optical fibers each coupled to corresponding output optical waveguide; and (3) photodetector array including photodetectors each located on the surface of the PLC and opposed to the corresponding junction between the output optical waveguide and output optical fiber.
Alternatively, the PLC module according to the present invention may comprise (1) a PLC provided with many waveguides including a plurality of input optical waveguides on a substrate, wherein input end faces of the input optical waveguides are slant against the optical axis thereof; (2) an optical fiber array including input optical fibers each coupled to the corresponding input optical waveguide; and (3) a photodetector array including photodetectors each located on the input optical fiber array and opposed to the corresponding junction between the input optical waveguide and input optical fiber.
In these PLC modules, a junction face between the input optical fiber and the input optical waveguide or between the output optical fiber and the output optical waveguide is slant against their optical axes, so that a part of signal light is reflected at this junction face. The reflected light is detected by a corresponding photodetector arranged in the photodetector array which is opposed to the junction face. As a consequence, power of the signal light can be accurately measured with a simple arrangement.
An angle between the junction face and the optical axis thereof is preferable within a range of 45 to 70 degrees, whereby the photodetectors can be located whereby the photodetectors can be displaced from a point directly above the junction faces, thus achieving a simple arrangement. Further, a distance between the junction face and the photodetector can be enlarged by providing the surface of the optical waveguide with a light-transmitting resin layer and arranging the photodetector on the resin layer. Therefore, the photodetector can be displaced, to an extent of the enlarged distance, toward the center of the substrate of the PLC from the point directly above the junction face, thus preferably achieving a simple arrangement.
A reflecting film may be disposed at the junction of the waveguides and the optical fibers, and the reflecting film is preferably a dielectric multi-layer film. Therefore, the reflected ratio at the junction can be kept constant and power of the signal light can be accurately measured with a simple arrangement.
The present invention can be suitably applied to a PLC comprising a multi-channel optical variable attenuator, an optical demultiplexer or an optical multiplexer. For example, in the application to the multi-channel optical variable atttenuator, power of light of each channel can be monitored so as to control power or attenuation of light emitted from each channel. Further, in the application to the optical demultiplexer or the optical multiplexer, light of each demultiplexed or mupltiplexed wavelenth can be monitored. It is natural that the present invention can be applied to a system comprising the multi-channel optical variable attenuator, the optical demultiplexer and the optical multiplexer.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.